The transfer is performed by the team clinician on the third day after the luteinising hormone surge and a maximum of two normally cleaving embryos are replaced according to our standard protocol. The luteal phase is supported as per randomization arm. Before the embryo transfer, the patient is interviewed by a designated research nurse who will explain the purpose of this study. Patients consenting to take part in the study will be assigned into one of the two study arms specified in an opaque envelope according to a computer-generated randomization list. The envelope will be read and injection (HCG or placebo as normal saline) given by a service nurse not involved in the study. Blood will be taken on day 6 after FET before the patient receives the second dose of HCG or placebo. A urine pregnancy test will be performed 16 days after the FET. In case of pregnancy, the outcome of pregnancy will be traced afterwards and used for analysis. Luteal phase support is not continued in those who get pregnant.